Wind turbine rotor

ABSTRACT

A wind turbine rotor, the rotor blades of which are shaped generally to resemble the sail of an Oceanic sprit rig sailboat (a traditional sailing craft with a sail plan having unusual and significant aerodynamic properties). The rotor blades might be movably mounted to maximize use of apparent wind. An alternative embodiment includes a contra-rotating rotor of similar design.

FIELD OF THE INVENTION

This invention relates to the rotors of wind-driven turbines. Morespecifically, it concerns rotors for those wind turbines that canproduce electrical power when linked to a generator.

BACKGROUND OF THE INVENTION

Humans have, for a very long time, tried to harness the kinetic energyin wind and put it to useful purposes. Numerous successful attempts atthis have produced valuable labor saving devices.

In modern times, the most sophisticated arrangements for harnessing windpower have resulted in electricity-producing wind turbines. This fieldof development is increasingly important. As concern about globalpetroleum supplies and prices continues to grow, and environmentalproblems associated with the burning of fossil fuels in general yieldanother set of worries, the promise of renewable and planet-friendlyenergy sources is immeasurably attractive.

Traditional wind turbines derive their power input by converting some ofthe wind's energy into a torque, or turning force, acting on a rotor.Rotor blades deflect the wind in a given direction and this causes therotor to rotate. Electrical power is produced when the turning force istransferred to a generator. The amount of energy that the wind transfersto the rotor depends upon the density of the air, the rotor area, andthe wind speed.

A successful and popular present-day wind turbine design is thethree-bladed tower. In this model, a housing, or nacelle, sits atop atall support tower. Attached to the front of the nacelle is a largethree-bladed rotor (similar to an airplane propeller). Housed within thenacelle are typically a gearbox and a generator. A nosecone covers thecenter of the rotor. Added features, such as variable pitch rotorblades, are sometimes included.

To keep the rotor perpendicular to the wind, a yaw mechanism isemployed. This can be a simple mechanical pivot or it can be asophisticated motorized setup. (If the rotor is not perpendicular to thewind, the wind turbine will be much less effective and “yaw error” issaid to result.)

The three-bladed rotor type of wind turbine can be costly to construct.Because taller turbines produce more power than shorter ones, largesupport towers must be built to derive the maximum benefit. In addition,due to the design of the propeller-like rotor, the rotor blades must bebuilt with enough strength to handle the stress loads they must endurein high winds, especially at the point where the three blades are joinedinside the nosecone.

In this “horizontal axis” design (wherein the rotor rotates around ahorizontal axis), the blades of the rotors face constant wind energywhen wind is present. It is possible, nevertheless, that an airplanepropeller, though good for propelling an aircraft through the sky, isnot the best design for a rotor intended to extract energy from wind.There are also numerous “vertical axis” wind turbine rotor designs thatcan be somewhat less efficient because some of the rotor blades areshielded from the wind by the other rotor blades at certain points inthe rotation cycle. On the other hand, these vertical axis turbines arewell-suited to be installed in locations where a horizontal axis designwould be inappropriate. Furthermore, vertical axis turbines typically donot have yaw error problems because their rotors are not orientedperpendicular to the wind direction.

All of these designs have merit and contribute significantly to thegreen energy revolution. Yet there remains room for improvement. Priorart wind turbines utilize merely the true wind energy acting upon theirrotor blades and cannot benefit from the apparent wind created by theirown rotational movement. This is a considerable limitation on theirperformance.

Comparing prior art wind turbines to sailboats illustrates this point.When sailing off the wind, as on a broad reach or run, a sailboat cansail no faster than the true wind speed. In theory it can absorb asubstantial portion of the energy from the wind it is in contact with,but the sailboat still cannot exceed the true wind speed when sailingdownwind (assuming no effect from water currents, waves, etc.). The sailis simply being pushed by the wind, similar to the way that the windpushes the rotors of prior art turbines.

When, however, sailing on a beam reach—the fastest point of sail—thevessel benefits both from the true wind speed and from the apparent windgenerated by the forward motion of the boat. The apparent wind is addedto the true wind to create a stronger diving force. The sails capturethis driving force and generate “lift”. Even when on a close reach thesailboat realizes this advantage.

The physics behind a sailboat's ability to sail against the wind isprobably best explained by the concept of “attached flow” (whereby theairflow over the leeward side of the sail attaches to the sail and pullsit along to avoid leaving a vacuum). But regardless of the explanationfor the principle, it might be that sailboats—because of their abilityto benefit from apparent wind—provide a more proper starting point forwind turbine rotor design. And wind turbine rotors having rotor bladesmodeled after the sail plan of one particular type of sailboatpotentially could result in a significant advancement in wind turbinetechnology. The present invention provides such an advancement; It isintended to yield an extremely efficient turbine rotor capable ofoperating safely in a variety of wind conditions while incorporating asimple construction, low production cost, a low maintenance cost, andsound structural integrity.

SUMMARY OF THE INVENTION

The present invention comprises a horizontal axis wind-driven turbinerotor which can be situated atop a tower or other suitable supportstructure. The innovation it offers results from the unique shape of therotor's blades.

The blades are shaped to resemble generally the sail of a traditionalsailing craft which is believed to have been developed by PacificIslanders many years ago. The native Pacific proa (a canoe-like boat)employed an exceptionally well-performing sail and sail supportstructure called the “Oceanic sprit rig”, sometimes also referred to asthe “Oceanic lateen rig” or the “crab claw rig” (presumably as a resultof the sail's resemblance to a crab's claw). These three terms will beused interchangeably herein.

The Oceanic lateen rig's sail possesses some unusual properties and hasbeen shown to be astonishingly effective at harnessing the wind's energyto propel a sailing craft over water. This is especially true when theboat is sailing on a beam reach.

While the issue is the subject of debate, it is believed by some thatthe sail of the crab claw rig develops lift under very differentaerodynamic principles than those of other sailing rigs, especially ascompared to the popular “Bermudan” rig which is used on most sailboatsmade today. The Oceanic sprit rig has been shown to be aerodynamicallysuperior to the Bermudan rig in many respects. [For a general discussionof the crab claw rig's benefits and the science behind it, see SailPerformance; Techniques to Maximize Sail Power, revised edition, by C.A. Marchaj (International Marine/McGraw-Hill 2003) pages 152 to 176]

The present invention exploits the remarkable aerodynamic properties ofthe Oceanic lateen rig and applies them to wind turbine technology toprovide an alternative wind turbine rotor design. The crab claw rig'ssail provides a model for the rotor blades of this new rotor. Itsupplements the prior art, thereby contributing to the overall effort toproduce electricity from wind power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an Oceanic sprit rig.

FIG. 2 a is a plan view of a sail from an Oceanic latten rig.

FIG. 2 b is a plan view of a variation of the Oceanic lateen rig's sail.

FIG. 2 c is a plan view of another variation of the Oceanic lateen rig'ssail.

FIG. 3 is a perspective view of a de-powered Oceanic lateen rig sail.

FIG. 4 is a front view of a preferred embodiment.

FIG. 5 is a front view of an alternative preferred embodiment withcontra-rotating rotors.

DETAILED DESCRIPTION AND OPERATION OF THE PREFERRED EMBODIMENTS

The basic design of the Oceanic sprit rig and its unique sail isdisplayed in FIG. 1. A sail 20 of the Oceanic lateen has anarrowhead-like profile with a deeper camber—or curve to the sail—at ornear a trailing edge 21. The camber gradually diminishes towards thetip, designated by arrow “A”, where it may disappear entirely. The sail20 has leading edges 22 forming the other two sides of the arrowhead,and the leading edges 22 lie generally in the same plane. Also, the sail20 is more or less symmetrical along its longitudinal axis.

When sailing upwind or on a beam reach, the tip is closer than thetrailing edge 21 to the direction the wind is coming from. That is, thetip is in general nearer to the front of the boat than is the trailingedge 21. Also, like other types of sails, the concave side of the sail20 always faces the wind. That is, the windward side of the sail 20 isconcave and the leeward side is convex.

For a sailboat, the sail of crab claw rig is typically made of a clothmaterial, like most other sails. As a result, the leading edges 22 mustbe affixed to rigid spars, or “sprits” (not shown). For purposes of thepreferred embodiments of the present invention, however, thecrab-claw-sail-like-rotor-blades can be manufactured from a rigid orsemi-rigid material of sufficient strength and durability. This might bethe most beneficial construction for many applications.

For certain embodiments, though, a pliant fabric material (supported byone or more spars of some sort) might be an appropriate construction.

In FIGS. 2 a, 2 b, and 2 c are shown plan views of three variations ofthe Oceanic lateen rig sail, all of which are suitable rotor bladedesigns for the wind turbine rotor of the present invention. In FIG. 2 athe leading edges 22 are slightly curved, the trailing edge 21 iscurved, and the tip (marked by arrow “A”) is pointed. In FIG. 2 b, theleading edges 22 have a greater curvature and the tip (marked by arrow“A”) is rounded. Also in FIG. 2 b, the trailing edge 21 is straight. InFIG. 2 c, the sail has a “delta wing” shape with straight leading edges22, a pointed tip (marked by arrow “A”), and a straight trailing edge21.

Any combination of these features are appropriate for the preferredembodiments of the present invention (i.e., straight leadingedges/rounded tip, or curved leading edges/pointed tip; curved trailingedges, straight trailing edges, or some mixing of the two). Specificoperating conditions, though, might dictate a preferred combination.What is important is that the blades for the rotor of the presentinvention have an arrowhead-like profile with maximum camber at or nearthe trailing edge (corresponding to the trailing edge of a crab clawrig's sail) and camber decreasing towards the tip of the rotor blade(which corresponds to the tip of the sail of the crab claw rig), wherethe camber can disappear entirely. Also, the leading edges(corresponding to the leading edges of the crab claw rig's sail) of therotor blades preferably lie in the same plane.

When sailing in strong winds, sailboats sometimes can be “overpowered”if they have too much sail area exposed to the wind or have sailstrimmed too tight for the conditions. This situation is usually remediedby easing lines to spill wind from the sail (or sails) and, in extremesituations, by reducing total sail area. On an Oceanic spritrigged-craft, the sail is “de-powered” by permitting the rigid spars atthe leading edges to move closer together, thus increasing the camber ofthe sail along more or less a centerline (the centerline extending fromthe tip of the sail to the trailing edge 21). The dramatic increase inthe camber of the sail resulting from this action apparently disruptsthe attached flow on the leeward side of the sail and moderates thelifting power of the sail.

This is illustrated in FIG. 3. The leading edges 22 of the sail 20 havemoved towards one another, resulting in increased camber which willde-power the rig. Indicative of the de-powering is the dramaticcurvature of the trailing edge 21. In FIG. 3, the concave side of thesail 20 is indicated by arrow “B”.

If a rotor blade of the rotor in this disclosure is capable of flexing,or folding, along more or less a centerline, it could mimic thede-powering of an Oceanic lateen rig's sail and thus de-power the windturbine rotor. This would be a valuable safety feature for handlingextreme winds.

A preferred embodiment of the present invention is depicted in FIG. 4(the side depicted being that which will face the wind). A wind turbinerotor 23 consists of struts or spokes 24 extending from a central hub25. Rotor blades 26 are situated at the end of each of the struts orspokes 24 opposite the central hub 25. The rotor blades 26 are shapedgenerally like the sail of a crab claw rig. The rotor blades 26 are alsooriented such that their tips are pointed somewhat towards the directionof rotation for the wind turbine rotor 23 (this direction of rotation isindicated in FIG. 4 as arrow “C”; i.e., counter-clockwise). Also, theconcave side of the rotor blades (corresponding to the concave side ofthe Oceanic sprit rig sail) substantially face the wind.

Because the lift generated by a Oceanic lateen rig's sail comes from theleeward—or convex—side of the sail, the rotor blades 26 are preferablymounted to the struts or spokes 24 by their concave sides only so as toensure that the leeward side of each of the rotors blades 26 remainsunobstructed. This will result in the cleanest air flow over the convexleeward surfaces.

[NOTE: the size of the rotor blades 26 relative to the struts or spokes24 and the wind turbine rotor 23 may vary from the depiction of FIG. 4.The rotor blades 26 can be larger or smaller, depending upon theparticular adaptation.]

Any number or combination of struts or spokes 24 can be included. Forexample, multiple struts or spokes 24 can support each of the rotorblades 26. To provide a stronger structure, the struts or spokes 24 canbe connected to one another by suitable means. Alternatively, a rim (notshown) can encircle the struts or spokes 24 and the rotor blades 26 canbe attached to the rim for added structural integrity.

Returning to FIG. 4 each of the rotor blades 26 have two leading edges27, and each of the rotor blades 26 is set such that one of theirleading edges 27 is closer than the other to the central hub 25.

In operation, as the wind turbine rotor 23 starts to rotate it willbegin to generate apparent wind which will increase the driving force(i.e., lift) produced by the rotor blades 26.

As for a still other embodiment, the struts or spokes 24 can beeliminated entirely and the rotor blades 26 can be affixed directly tothe central hub 25.

In addition, the rotor blades 26 can be movably mounted such that, asthe rotational speed of the wind turbine rotor 23 increases, the rotorblades 26 will themselves turn so that their tips face even closer tothe direction of the apparent wind. This would permit the rotor blades26 to benefit to the fullest extent from the apparent wind for achievingmaximum lift.

In FIG. 4 the wind turbine rotor 23 has three evenly-spaced rotor blades26 arranged to substantially balance forces when operating. But thenumber of rotor blades 26 can vary for different applications.Embodiments of the present invention may have any number, even or odd,of rotor blades 26 as deemed appropriate. Experimentation will yieldinsight as to the arrangement providing superior performance for a givensituation. There might even be an application where only one rotor bladeis appropriate, though the best designs attempt to balance forces toensure safety and stability in high wind situations.

Furthermore, the rotor of the present invention may also include rotorblades of other designs in combination with theOceanic-sprit-rig-sail-shaped-rotors.

A significant advantage offered by the FIG. 4 embodiment is that theturning force is generated as far as possible from the central hub 25.The turning force the rotor blades 26 generate therefore benefits fromleverage. This results in greater usable torque at the central hub 25for producing electrical power if the present invention is coupled to agenerator.

As for other embodiments, the wind turbine rotor of the presentinvention can have a lattice-like structure consisting of multiplestruts or spokes. The advantage of the lattice construction being thatthe overall strength of the wind turbine rotor can be increased bybuttressing high stress load areas. The “airplane propeller” rotor bladecannot increase thickness at the high stress point near the central hubbecause to do so would decrease the aerodynamic efficiency of the rotorblade. But the wind turbine rotor of the preferred embodiments can workwith struts or spokes with reinforcing support at high stress areas.

The lattice construction can even take the form of a crisscrossingspokes “bicycle wheel-like” arrangement, resulting in a light and strongstructure.

Another advantage of the lattice construction is that a second windturbine rotor of the present invention can be housed within thelattice-like structure of a larger one. The two wind turbine rotorscould then work in combination to generate electricity. For example, oneof the wind turbine rotors could rotate in a clockwise direction and thesecond wind turbine rotor could be arranged to rotate in the oppositedirection. If one of the wind turbine rotors is connected to the rotorof an electrical generator, and the second of the wind turbine rotors isconnected to the stator of the same generator, then the relative motionof the generator's rotor relative to its stator would increase. Thiswould maximize the electricity-generating capacity.

One example of this contra-rotating embodiment is displayed in FIG. 5,shown as it will face the wind. A first rotor 30 has a latticeconstruction support structure as previously described. The latticesupport structure includes a circular rim 31 for added strength. Thefirst rotor 30 also has four rotor blades 32. A second four-bladed windturbine rotor 33 sits nestled within the lattice construction supportstructure of the first rotor 30. In operation, the first rotor 30, asdepicted here, would rotate counter-clockwise and the second four-bladedwind turbine rotor 33 would rotate clockwise.

Alternatively, the second four-bladed wind turbine rotor 33 can simplybe mounted in front of or behind the first rotor 30, while stillemploying the contra-rotating element. Also, the number of rotors bladesfor each or the rotors can vary, and rotor blades of other designs canbe included.

Other alterations to the preferred embodiments are possible. Forexample, a wind turbine with a rotor design of the present inventionmight be made foldable such that it can be transported to a variety oflocations. Also, many different sizes of rotors are possible. A smallerrotor might be set up atop the roof of an electrically-poweredautomobile to recharge the vehicle's batteries when it is parked, whilelarger rotors could be made for permanent wind turbines that provideelectricity for homes or offices. Furthermore, sensors can be employedto help optimize rotor blade angle relative to the apparent wind.

Although the description above contains several specificities, theseshould not be construed as limits on the scope of the present invention.The details given are intended merely to provide illustrations of someof the presently preferred embodiments. It is to be therefore understoodthat many changes and modifications by one of ordinary skill in the artare considered to be within the scope of the invention. Thus, the fullscope should be determined by the appended claims and their legalequivalents, rather than by examples given.

1) A wind turbine rotor; the wind turbine rotor having at least onerotor blade shaped to resemble generally the sail of an Oceanic spritrig. 2) The wind turbine rotor of claim 1, wherein the at least onerotor blade shaped to resemble generally the sail of an Oceanic spritrig is manufactured from a rigid or semi-rigid material, or from apliant fabric material. 3) The wind turbine rotor of claim 1, whereinthe at least one rotor blade shaped to resemble generally the sail of anOceanic sprit rig is movably mounted to the wind turbine rotor. 4) Thewind turbine rotor of claim 1, wherein the at least one rotor bladeshaped to resemble generally the sail of an Oceanic sprit rig isattached to a strut or spoke opposite a central hub. 5) The wind turbinerotor of claim 1, in combination with a second, contra-rotating, rotor.6) The wind turbine rotor of claim 1, wherein the at least one rotorblade shaped to resemble generally the sail of an Oceanic sprit rig iscapable of flexing or folding to increase camber. 7) A wind turbinerotor; the wind turbine rotor having one or more rotor blades; at leastone of the one or more rotor blades resembling generally the sail of anOceanic lateen rig. 8) The wind turbine rotor of claim 7, wherein theone or more rotor blades is/are manufactured from a rigid or semi-rigidmaterial, or from a pliant fabric material. 9) The wind turbine rotor ofclaim 7, wherein the one or more rotor blades is/are movably mounted tothe wind turbine rotor. 10) The wind turbine rotor of claim 7, whereinthe one or more rotor blades is/are attached to struts or spokesopposite a central hub. 11) The wind turbine rotor of claim 7, incombination with a second rotor that rotates in the opposite direction.12) The wind turbine rotor of claim 7, wherein at least one of the oneor more rotor blades is capable of flexing or folding for de-powering.13) A wind turbine rotor; the wind turbine rotor having rotor blades;some or all of the rotor blades resembling generally the sail of a crabclaw rig. 14) The wind turbine rotor of claim 13, wherein the rotorblades are arranged to substantially balance forces when operating inwind. 15) The wind turbine rotor of claim 13, wherein one or more of therotor blades is/are manufacture from a rigid or semi-rigid material. 16)The wind turbine rotor of claim 13, wherein one or more of the rotorblades is/are movably mounted to the wind turbine rotor. 17) The windturbine rotor of claim 13, arranged in combination with a second,contra-rotating, rotor; the second, contra-rotating, rotor having one ormore rotor blades resembling generally the sail of a crab claw rig. 18)The wind turbine rotor of claim 13, wherein one or more of the rotorblades is/are capable of flexing or folding along more or less acenterline for de-powering.